I always like the very diplomatic way the Catholic Church says things...
Marriage, Divorce, and Mixed Marriages
"Though the Church would prefer that all Orthodox Christians would marry Orthodox Christians, it does not insist on it in practice. Out of its concern for the spiritual welfare of members who wish to marry a non-Orthodox Christian, the Church will conduct a "mixed marriage." For this purpose, a "non-Orthodox Christian" is a member of the Roman Catholic Church, or one of the many Protestant Churches which believe in and baptize in the name of the Holy Trinity. This means that such mixed marriages may be performed in the Orthodox Church. However, the Orthodox Church does not perform marriages between Orthodox Christians and persons belonging to other religions, such as Islam, Judaism, Buddhism, Hinduism, or any sectarian and cult group, such as Christian Science, Mormonism, or the followers of Rev. Moon."
Yup. Just like Jesus.